A fuel system in an aircraft is designed to supply high pressure fuel to the engines which power the aircraft. Typical gas turbine engine fuel supply systems include a fuel source, such as a fuel tank, and one or more pumps. The one or more pumps draw fuel from the fuel tank and deliver pressurized fuel to one or more primary fuel loads and to one or more secondary fuel loads via one or more supply lines. Generally, the primary fuel loads, which include the fuel manifolds in the engine combustor, are supplied with fuel via, for example, a priority flow line. The secondary fuel loads, which may include a motive flow valve and regulator, one or more variable geometry actuators, and one or more bleed valves, are supplied with fuel via, for example, a secondary flow line.
The priority flow line may include one or more valves in flow series between the pumps and the fuel manifolds. These valves generally include at least a metering valve and a pressurizing valve. The metering valve is typically configured to control priority flow to the one or more primary fuel loads. The pressurizing valve, which is typically disposed downstream of the metering valve, functions to maintain a minimum system pressure magnitude in portions of the supply lines. More specifically, the pressurizing valve typically maintains pump discharge backpressure above a minimum pressure magnitude.
Though highly unlikely, it is postulated that a loss or increase of metered burn flow to an engine could occur. Hence, many aircraft fuel systems are designed with a thrust control override system to accommodate this postulated event. The intended effect of a thrust control override system is to set the burn flow rate to the engine at a predetermined constant flow rate, typically near an engine idle condition. This is because it is desirable to have the engine at idle speed verses shutting the engine down, thereby allowing the engine to continue to drive electrical generators and various other loads. However, most thrust control override systems presently known are relatively complex, and thus relatively costly.
Hence, there is a need for a thrust control override system that is less complex and/or costly as compared to presently known systems. The present invention addresses at least this need.